So? What numbers do I look at? Only Top tube? I really don’t understand. They both don’t even measure the exact same things. Please help!
Bob
A picture is worth a thousand words. For an example go on the Cervelo site and look at their frame geometry diagrams. That should give you a good idea of what you want to look for.
Really good question and not easy to answer. You need a pretty good understanding of frame geometry and what seemingly small changes do to the handling and fit of a frame.
For instance, toptube length without seat tube angle (or, setback … which I think is a more useful number) doesn’t tell you much, if anything. Two frames with the same toptube length but seattube angles just one degree off won’t fit the same (although with seatpost and stem choices they can be made to fit the same).
The best treatise on the subject was published in the early 70s by the Italian sports committee. It’s called the CONI Manual and it really is the bible for bike fit.
Here’s the situation. I have a 55 P3 that is too long in the top tube when I am fit properly, which is 75 deg on it. So I was going to get a 55 Blade which I was told by two trusted fitters would fit me. But I want a TCR TT. Its compact as you know. So how do I compare these two? There isn’t a diagram on the Litespeed page like there is at Giant
What you are talking about is “effective” top tube length and has to be measured on an imaginary horizontal line, not along the actual downsloping head tube on a compact frame. This is how Giant would measure their top tubes I’d suspect. Realize also that you also have a certain degree of adjustability with playing with stem length.
With the Lightspeed your best bet may be to give them a call and explain your situation.
My guess is that you’re around 5’10ish. The 55cm P3 is going to be too big, you’ll need either a 52cm or upgrade to a 54cm P3C.
The Litespeed 55cm has a very comfy TT length, but perhaps long at your STA. If you’re riding a bit slack, you are better served by the QR TiPhoon (54cm at 76.5 degrees). I bet this is your bike!!!
IMO, the Giant TT is tricky as mentioned in your other thread…
Hitting people in the mouth is much simpler than trying to understand frame geometries. Stick with Fight Club (unless of course the bike is to be part of Project Mayhem).
You forgot the first rule of Project Mayhem.